A commonly used gas-fired water heater is the storage type, generally comprising an assembly of a water tank, a main gas burner to provide heat to the tank, a standing pilot burner to initiate the main burner on demand, an air inlet adjacent the burner near the base of the jacket, an exhaust flue and a jacket to cover these components. Another type of gas-fired water heater is the instantaneous type which has a water flow path through a heat exchanger heated, again, by a main burner initiated from a pilot burner flame. For convenience, the following description is in terms of storage type water heaters. However, the invention is not limited to this type.
A particular difficulty with many locations for water heaters is that they are also used for storage of other equipment such as lawn mowers, trimmers, snow blowers and the like. It is common for such machinery to be refueled in such locations.
There have been a number of reported instances of spilled gasoline and associated fumes being accidentally ignited. There are many available ignition sources, such as refrigerators, running engines, electric motors, electric light switches and the like. However, gas water heaters have sometimes been suspected because they often have a continuously burning pilot flame and combustion air inlets disposed at or near floor level, where spillage may occur.
To contain ignitions that may occur due to the accidental spillage of fuel near a gas fired water heater, many manufacturers have incorporated flame traps into the design of their water heater. An example of such a design is disclosed in U.S. Pat. No. 6,293,230 to Valcic et al. The flame traps used in such designs comprise ports sized and shaped to cause air and extraneous fumes to pass through the ports at a velocity higher than the flame velocity of the extraneous fumes, thereby confining ignition and combustion of the extraneous fume species within the combustion chamber.
One potential problem associated with the ports of the flame arresters is that the ports may become clogged with lint, dust, oil or any other element that may become disposed in or around the ports. When the ports become clogged, there is a potential for the combustion of the burner to burn inefficiently and produce increased levels of CO.
One general consequence to both the emission of CO and the ignition of vapors is that the temperature in the combustion chamber rises above a normal operating level. It would be beneficial to provide a water heater with an improved system for detecting a rise in temperature in the combustion chamber and cut the fuel to the burner, thereby terminating combustion in the combustion chamber.